Power supply device and lighting equipment provided with power supply device

ABSTRACT

A power supply device according to one embodiment is configured to control a lighting of semiconductor light-emitting elements, wherein a dimming signal is canceled during a predetermined time period (T) from a timing immediately after power-ON, so as to light on light-emitting diodes to have a predetermined light amount, for example, a minimum light amount. After an elapse of the predetermined time period (T), cancellation of the dimming signal is released to light on the light-emitting diodes to have a light amount instructed by the dimming signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of Ser. No. 12/873,759 filed on Sep.1, 2010 which is a continuation application of PCT Application No.PCT/JP2009/055873, filed Mar. 24, 2009, which was published under PCTArticle 21(2) in Japanese.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2008-076837, filed Mar. 24, 2008.

The entire contents of the above noted applications are incorporatedherein by reference.

FIELD

Embodiment described herein relate generally to a power supply devicesuited for driving a semiconductor light-emitting element such as alight-emitting diode, and a lighting equipment provided with this powersupply device.

BACKGROUND

Recently, as a power supply for driving a semiconductor light-emittingelement such as a light-emitting diode, a power supply device whichswitches a DC power using a switching element is popularly used.

A power supply device of this type is often used in a lighting equipmenthaving a dimming function that can arbitrarily control an amount oflight of a light source for lighting in, e.g., a store. Such lightingequipment generally uses a four-wire dimming system as a dimming system.This is because since a large number of lighting equipments are used in;e.g., a shore, the four-wire dimming system is free from any problem ofgenerating harmonics in input currents unlike a dimming system based onphase control, and is suited to simultaneously operating a large numberof equipments.

In a power supply device of the four-wire dimming system, a dimmingoperation member is integrally provided to a so-called wall switchgenerally allocated on a wall surface. To a mechanical switch of thedimming operation member, a dimming signal generator, which supplies adimming signal to a load via a feeder terminal, is connected. Thisdimming signal generator outputs a dimming signal, which is supplied toeach lighting equipment. In such power supply device, when the userturns on the mechanical switch of the dimming operation member, a powersupply of a lighting equipment is turned on, and a power supply of thedimming signal generator is also turned on at the same time.

No problem is posed when the ON operation of the mechanical switch turnson (power-activates) the power supply of the dimming signal generatorsimultaneously with power-ON (power activation) of the lightingequipment, so as to immediately output a dimming signal, thussimultaneously attaining lighting and dimming of the lighting equipment.However, when the lighting equipment is lighted on before the dimmingsignal is output, the lighting equipment is lighted on for a certainperiod in a state the dimming signal is not input before the lightingequipment is controlled to a desired light amount by the dimming signal.In general, since the lighting equipment is set to light on in a fulllight state when no dimming signal is input, it is lighted on in a fulllight state only for a moment, and then transits to a dimmed state.

Since a lighting circuit of a general electric discharge lamp forms anadvanced preheating state immediately after power activation, and is setintentionally not to light on a lamp for a while, no serious problem isposed. However, in a lighting equipment which uses a semiconductorlight-emitting element such as a light-emitting diode as a recent lightsource, a phenomenon of causing a full light state only for a momentimmediately after activation due to a delay of a dimming signal readilyoccurs, resulting in unnatural lighting transition as the lightingequipment. Hence, the merchantability of the lighting equipment isseriously impaired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a lighting equipmenthaving a power supply device according to the first embodiment;

FIG. 2 is a schematic sectional view showing the internal structure ofthe lighting equipment shown in FIG. 1;

FIG. 3 is a schematic circuit diagram showing an electrical circuit ofthe power supply device shown in FIG. 1;

FIG. 4A is a timing chart for explaining the operation of the powersupply device shown in FIG. 3;

FIG. 4B is a timing chart for explaining the operation of the powersupply device shown in FIG. 3;

FIG. 4C is a timing chart for explaining the operation of the powersupply device shown in FIG. 3;

FIG. 4D is a timing chart for explaining the operation of the powersupply device shown in FIG. 3;

FIG. 4E is a timing chart for explaining the operation of the powersupply device shown in FIG. 3; and

FIG. 5 is a circuit diagram showing a circuit of a power supply deviceaccording to the second embodiment.

DETAILED DESCRIPTION

A power supply device and a lighting equipment provided with this powersupply device according to an embodiment of the present invention willbe described hereinafter with reference to the drawings.

In general, according to one embodiment, a power supply device comprisesa DC output generation module, a semiconductor light-emitting element,and a control module. The DC output generation module is configured toreceive an AC power, convert the AC power into a DC power, and outputthe DC power. The semiconductor light-emitting element is supplied withthe DC power output from the DC output generation module, and emitslight. The control module is configured to receive a dimming signal, andcontrol the DC power output from the DC output generation module inaccordance with the dimming signal. The control module controls the DCoutput generation module to dim and light on or off the semiconductorlight-emitting element by canceling control of the DC power based on thedimming signal during a predetermined time period from a timingimmediately after the AC power is supplied.

First Embodiment

FIGS. 1 and 2 show a lighting equipment which incorporates a powersupply device according to an embodiment of the present invention.Referring to FIGS. 1 and 2, reference numeral 1 denotes an equipmentmain body. This equipment main body 1 is prepared by die-castingaluminum, and is formed into a nearly cylindrical shape having openingsat two ends. The interior of this equipment main body 1 is partitionedinto three spaces in a vertical direction by partition members 1 a and 1b. In a lower space between a lower opening and the partition member 1a, a light source unit 2 is arranged. This light source unit 2 includesa plurality of LEDs 2 a as semiconductor light-emitting elements and areflector 2 b for reflecting light rays from the LEDs 2 a. The pluralityof LEDs 2 a are mounted in the lower space, and are allocated at equalintervals along a circumferential direction of a disk-shaped circuitboard 2 c arranged on the lower surface of the partition member 1 a.

A hollow space between the partition members 1 a and 1 b of theequipment main body 1 is assigned to a power supply chamber 3. In thispower supply chamber 3, a circuit board 3 a is arranged on an upperportion of the partition member 1 a. On this circuit board 3 a,electronic components which configure a power supply device required todrive the plurality of LEDs 2 a are arranged. This DC power supplydevice and the plurality of LEDs 2 a are connected via lead wires 4.

A space between the partition member or plate 1 b and an upper openingof the equipment main body 1 is defined as a power supply terminalchamber 5. In this power supply terminal chamber 5, a power supplyterminal block 6 is arranged on the partition member 1 b. This powersupply terminal block 6 is a terminal block required to supply an ACpower of a commercial power supply to the power supply device in thepower supply chamber 3, and has outlets 6 b as power supply terminalsfor a power supply cable, outlets 6 c used as terminal portions for afeeder cable, a release button 6 d used to release a power supply lineand feeder line, and the like on two surfaces of a box 6 a which is madeup of an electrically insulating synthetic resin.

FIG. 3 is a circuit diagram of the power supply device according to theembodiment of the present invention, which is incorporated in the powersupply chamber 3 of the lighting equipment with the above arrangement.

Referring to FIG. 3, reference numeral 11 denotes an AC power supply asa commercial power supply outside the lighting equipment. This AC powersupply 11 is connected to power supply terminals 6 b of the lightingequipment shown in FIG. 2 via a lighting switch (not shown) outside thelighting equipment, and a noise filter circuit 14 including a capacitor12 and inductor 13 is connected to the power supply terminals 6 b. Inthis noise filter circuit 14, the capacitor 12 is connected in parallel,and a full-wave rectifying circuit 15 is connected via the inductor 13between the power supply terminals. The full-wave rectifying circuit 15outputs a rectified voltage VDC which is obtained by full-waverectifying an AC power from the AC power supply 11 in response to ON ofthe lighting switch, as shown in FIG. 4A. Between the output terminalsof the full-wave rectifying circuit 15, a smoothing capacitor 16 whichsmoothes a ripple current is connected in parallel. The noise filtercircuit 14, full-wave rectifying circuit 15, and capacitor 16 form a DCpower supply circuit, which is connected to a primary winding 17 a of aswitching transformer 17 as a flyback transformer.

To the primary winding 17 a of the switching transformer 17 a as aflyback transformer, a field effect transistor (FET) 18 as a switchingelement is connected in series. To the two terminals of the smoothingcapacitor 16, a series circuit of the primary winding 17 a of theswitching transformer 17 and FET 18 is connected. The switchingtransformer 17 has a secondary winding 17 b and tertiary winding 17 c,which are magnetically coupled to the primary winding 17 a.

To the two terminals of the primary winding 17 a of the switchingtransformer 17, a snubber circuit 22 is connected. This snubber circuit22 includes a capacitor 19, resistor 20, and an anti-backflow diode 21.The capacitor 19 and resistor 20 are connected in parallel, and theparallel circuit of the capacitor 19 and resistor 20 is connected to anode between the primary winding 17 a of the switching transistor 17 andthe FET 18 via the diode 21. This snubber circuit 22 absorbs a flybackvoltage generated at the primary winding 17 a of the switchingtransformer 17, absorbs a ringing voltage generated due to a leakageinductance, and regenerates a current flowing through the primarywinding 17 a when the FET 18 is disabled. That is, when a flybackvoltage is generated, it charges the capacitor 19, and the capacitor 19discharges the charged voltage via the resistor 20 when the flybackvoltage disappears, thus absorbing the flyback voltage by the snubbercircuit 22. When a ringing voltage is generated in a leakage inductanceof the switching transformer 17, it is used to charge the capacitor 19,and is absorbed by the capacitor 19.

To the secondary winding 17 b of the switching transformer 17, arectifying/smoothing circuit 25 which rectifies and smoothes a voltagegenerated at the secondary winding 17 b is connected. Therectifying/smoothing circuit 25 includes a diode 23 connected in seriesto the secondary winding 17 b, and a smoothing capacitor 24 connected inparallel to the secondary winding 17 b. Together with the snubbercircuit 22, FET 18, and switching transformer 17, thisrectifying/smoothing circuit 25 forms a DC lighting circuit forgenerating a DC output required to light on the light-emitting diodes.

In this DC lighting circuit, when the FET 18 is turned on and off inresponse to pulse signals having a certain ON duty ratio output from acontrol circuit 44, a DC voltage from the full-wave rectifying circuit15 is converted into a rectangular wave voltage, which is applied to theprimary winding of the switching transformer 17. When this rectangularwave voltage appears at the primary winding of the switching transformer17, a boosted AC voltage is generated from the secondary winding 17 b ofthe switching transformer 17. This AC voltage is rectified by the diode23 of the rectifying/smoothing circuit 25, the rectified voltage issmoothed by the smoothing capacitor 24, and the smoothed voltage isoutput from the smoothing capacitor 24 as a DC output.

To the two terminals of the smoothing capacitor 24 of therectifying/smoothing circuit 25, a plurality of (for example, four)series-connected light-emitting diodes 26 to 29 (corresponding to theLEDs 2 a as light sources shown in FIG. 1) as semiconductorlight-emitting elements are connected as loads. The series-connectedlight-emitting diodes 26 to 29 are dimmed and lighted on when they aresupplied with a DC current according to a certain DC voltage output fromthe rectifying/smoothing circuit 25. That is, when the FET 18 is turnedon and off in response to switching pulses having a high ON duty ratio,an AC voltage, which is boosted to a relatively high level, appears fromthe secondary winding 17 b of the switching transformer 17, a relativelyhigh DC voltage is applied from the rectifying/smoothing circuit 25 tothe light-emitting diodes 26 to 29, and a constant current is suppliedto the light-emitting diodes 26 to 29, which are lighted on at a certainluminance level. When the FET 18 is turned on and off in response toswitching pulses having a low ON duty ratio, an AC voltage, which isboosted to a relatively low level, appears from the secondary winding 17b of the switching transformer 17, and a relatively high DC voltage isapplied from the rectifying/smoothing circuit 25 to the light-emittingdiodes 26 to 29, thus dimming and lighting on the light-emitting diodes26 to 29.

To the tertiary winding 17 c of the switching transformer 17, arectifying/smoothing circuit including a diode 30 and capacitor 31 isconnected. The diode 30 is connected in series to a terminal of thetertiary winding 17 c to rectify an AC output generated at the tertiarywinding 17 c. The capacitor 31 is connected in parallel to the tertiarywinding 17 c via the diode 30, smoothes a rectified output from thediode 30, and outputs the smoothed output as a DC voltage. Thisrectifying/smoothing circuit connected to the tertiary winding 17 cfunctions as a circuit for detecting voltage application to thelight-emitting diodes 26 to 29, and outputs a rectified voltage insynchronism with a voltage output from the rectifying/smoothing circuit25 connected to the secondary winding 17 b.

To the capacitor 31, a series circuit of a resistor 32 and aphototransistor 332 of a photocoupler 33 is connected in parallel. Thephotocoupler 33 is configured by housing a light-emitting diode 331 andthe phototransistor 332, which are electrically isolated from each otherand are optically joined, in a single package. Light emitted by thelight-emitting diode 331 is received by the phototransistor 332 toconduct the phototransistor 332. The light-emitting diode 331 of thephotocoupler 33 is connected to a rectifying circuit 35, which isconnected to input terminals 6 c (corresponding to the outlets 6 c usedas feeder cable terminal portions). The input terminals 6 c areconnected to a dimming operation member 34 arranged on, e.g., a wallsurface outside the lighting equipment. The dimming operation member 34includes a PWM generator (not shown) for generating a PWM dimming signalused to set a dimming depth, and supplies a PWM dimming signal to therectifying circuit 35 via the input terminals 6 c in response to ON ofthe lighting switch. Therefore, the light-emitting diode 331 isactivated to emit light during an ON duty period of the PWM dimmingsignal, and the phototransistor 332 is conducted during that period. ThePWM dimming signal can change a duty ratio of a pulse-shaped signalaccording to a user operation at the dimming operation member 34,thereby setting a dimming depth according to this duty ratio.

To the capacitor 31, a series circuit of a capacitor 36 and resistor 37is connected in parallel. The series circuit of the capacitor 36 andresistor 37 forms a differentiating circuit, and generates, based on avoltage output from the capacitor 31, a differentiated output at a nodebetween the capacitor 36 and resistor 37 only for a predetermined timeperiod T. This predetermined time period T is set to be longer than amaximum delay time TD. In this case, the maximum delay time TD isdefined as a period after the lighting switch is turned on and anelectric power is supplied from the power supply 11 until a dimmingcontrol start timing at which a dimming signal is output. To theresistor 37, a diode 38 is connected in parallel to have a polarityshown in FIG. 3. This diode 38 is arranged to remove a charge from thecapacitor 36 of the differentiating circuit.

To the node between the capacitor 36 and resistor 37, the base of atransistor 39 as a switching element is connected. The emitter of thistransistor 39 is grounded, and the collector is connected to a positiveinput terminal of an operational amplifier 40. The transistor 39 isenabled only for the predetermined time period T in response to thedifferentiated output generated at the node between the capacitor 36 andresistor 37. Between ground and a node A between the resistor 32 andphototransistor 332, a series circuit of a resistor 41 and capacitor 42is connected. A node B between the resistor 41 and capacitor 42 isconnected to the collector of the transistor 39, and also to thepositive input terminal of the operational amplifier 40. To the node Abetween the resistor 32 and phototransistor 332, a dimming signal (VDIM)shown in FIG. 4B, which is output by the light-emitting diode 331 and isreceived by the phototransistor 332, is output. To the node B betweenthe resistor 41 and capacitor 42, a dimming out (Vdet) shown in FIG. 4C,which is obtained by smoothing the dimming signal (VDIM) by thecapacitor 42, is output.

A negative input terminal of the operational amplifier 40 is connectedto its output terminal, which is connected to the control circuit 44 viaa diode 43 having a polarity shown in FIG. 3. To the control circuit 44,a reference voltage source Vref is connected via a diode 45 having apolarity shown in FIG. 3. These diodes 43 and 45 form an OR circuit, andtheir node C outputs a larger one of a signal from the operationalamplifier 40 and a reference signal Vref to the control circuit 44 as acontrol signal Vcont, as shown in FIG. 4E.

The control circuit 44 turns on and off the FET 18 by an operationaccording to the control signal Vcont to switching-drive the switchingtransformer 17, thereby controlling an output supplied to thelight-emitting diodes 26 to 29. The control circuit 44 is configured bya switching pulse generation circuit whose ON duty ratio is determinedaccording to the level of the control signal Vcont. For example, thecontrol circuit 44 includes a memory which is referred to by the controlsignal Vcont, an arithmetic circuit which generates pulse signals at anON duty ratio stored in this memory, and an amplifier which amplifiespulses output from this arithmetic circuit.

The operation of the circuit shown in FIG. 3 will be described below.

Assume that the dimming operation member 34 is set in advance by theuser in a state in which the dimming signal member 34 is ready to outputa dimming signal having a certain dimming depth, and is set to, forexample, light on the light-emitting diodes 26 to 29 by dimming them toa certain intermediate dimming level. Also, assume that the referencesignal Vref is set at a level required to light on the light-emittingdiodes 26 to 29 at a fixed level, e.g., to have a minimum light amount,as shown in FIG. 4D.

At a timing t0 in a state in which illuminating light can be dimmed inthis way, the lighting switch provided to the dimming operation member34 is operated to turn on (power-activate) the power supply of thelighting equipment, and the power supply of the dimming signal generator34 is also turned on simultaneously with this ON operation. At thistiming to, in response to power-ON of the lighting equipment, an ACpower of the AC power supply 11 is supplied to the full-wave rectifyingcircuit 15, which outputs a DC voltage shown in FIG. 4A to the ripplecurrent smoothing capacitor 16. This voltage output is applied to theseries circuit of the primary side of the switching transformer 17 andthe FET 18 in an OFF state. At this timing t0, the FET 18 is set in anOFF state since it is not ON, and no DC voltage is applied to theprimary side of the switching transformer 17. As will be describedlater, after an elapse of a certain delay time TD, the FET 18 is turnedon and off, and the DC voltage is applied to the primary side of theswitching transformer 17.

Also, at the timing t0, the reference signal Vref shown in FIG. 4D isinput to the control circuit 44 as the control signal Vcont shown inFIG. 4E via the diode 45. Therefore, the control circuit 44 begins todrive the FET 18 in response to the control signal Vcont having a levelof the reference signal Vref. That is, the control circuit 44 generatespulse signals having an ON duty ratio specified by the level of thereference signal Vref with reference to the level of the referencesignal Vref, and applies the pulse signals to the gate of the FET 18. Inthis case, from the timing t0, the control circuit 44 begins to outputthe pulse signals, as shown in FIG. 4A. The FET 18 is turned on andconducted during an ON period specified by the ON duty ratio, and iskept OFF during an OFF period specified by the ON duty ratio. When theFET 18 is turned on and off in response to the pulse signals, a DCvoltage output from the rectifying/smoothing circuit is switched and isconverted into a rectangular wave. This rectangular wave is applied tothe switching transformer 17. Therefore, the switching transformer 17 isswitching-driven. More specifically, in response to an ON operation ofthe FET 18, a current is supplied to the primary winding 17 a of theswitching transformer 17 to accumulate an energy. In response to an OFFoperation of the FET 18, the energy accumulated on the primary winding17 a is discharged via the secondary winding 17 b. Therefore, from theprimary winding 17 b of the switching transformer 17, an AC outputvoltage is supplied to the rectifying/smoothing circuit 25, and isconverted into a DC voltage output by the rectifying/smoothing circuit25. This DC voltage output is applied to the light-emitting diodes 26 to29. Therefore, the light-emitting diodes 26 to 29 are lighted on to havea minimum light amount set as the reference signal Vref.

When an AC voltage is output from the secondary winding 17 b of theswitching transformer 17, an AC voltage output is also generated at thetertiary winding 17 c of the switching transformer 17. This AC voltageis rectified and smoothed by the diode 30 and capacitor 31, and a DCoutput is generated across the two terminals of the capacitor 31.Therefore, the DC voltage is applied to the differentiating circuitformed by the capacitor 36 and resistor 37. Upon application of this DCvoltage, a differentiated output is generated at the node between thecapacitor 36 and resistor 37 from a timing t1 during a time period(T-TD) obtained by subtracting the delay time from the predeterminedtime period T, more properly, only during a period from the timing t1 toa timing t2. This differentiated output is applied to the gate of thetransistor 39 to enable the transistor 39. Therefore, the node B betweenthe resistor 41 and capacitor 42 is grounded, and the positive inputterminal of the operational amplifier 40 is also grounded.

Also, at the timing t1 delayed from power-ON of the lighting equipmentby the switch operation of the dimming operation member 34 by the delaytime period TD, the dimming signal generator 34 generates a PWM dimmingsignal VDIM. For example, at the timing t1 after the delay time TD, asshown in FIG. 4B, with respect to the voltage output shown in FIG. 4A ofthe ripple current smoothing capacitor 16, the PWM dimming signal (VDIM)is generated at the node A between the resistor 32 and phototransistor332. However, since the node B between the resistor 41 and capacitor 42is grounded because the transistor 39 is enabled during the time period(T-TD) after the delay time period TD, this PWM dimming signal (VDIM) isnot output to the node B, a PWM dimming output (Vdet) is canceled duringthis predetermined time period T, more properly, during the time period(T-TD), as shown in FIG. 4C, and the operational amplifier 40 does notgenerate any dimming output of the level according to the PWM dimmingsignal (VDIM). Therefore, the light-emitting diodes 26 to 29 are lightedon to have a minimum light amount by the operation of the controlcircuit 44 which receives the reference signal Vref, as described above.

After that, at the timing t2 when the predetermined time period T iselapsed, the differentiated output that appears at the node between thecapacitor 36 and resistor 37 disappears, thus disabling the transistor39. Therefore, the PWM dimming signal (VDIM) which appears at the node Abetween the resistor 32 and phototransistor 332 is transmitted to thenode B between the resistor 41 and capacitor 42, thus generating thedimming output (Vdet), as shown in FIG. 4C. As a result, the dimmingoutput (Vdet) is amplified by the operational amplifier 40, and is inputto the control circuit 44 via the diode 43. Since this dimming output(Vdet) is larger than the reference signal Vref shown in FIG. 4D, thedimming output (Vdet) is input to the control circuit 44. Therefore, thecontrol circuit 44 generates pulse signals having an ON duty ratiospecified according to the level of the dimming output (Vdet), andapplies them to the gate of the FET 18. The FET 18 is turned on and offin response to the pulse signals having the ON duty ratio according tothe level of the dimming output (Vdet). Therefore, an AC output voltageis supplied from the secondary winding 17 b of the switching transformer17 to the rectifying/smoothing circuit 25, and is converted into a DCvoltage output by the rectifying/smoothing circuit 25. This DC voltageoutput is applied to the light-emitting diodes 26 to 29. Therefore, thelight-emitting diodes 26 to 29 are lighted on to have a light amountspecified according to the level of the dimming output (Vdet).

In the circuit shown in FIG. 3, a dimming signal is canceled during thepredetermined time period T from a timing immediately after power-ON,and the light-emitting diodes 26 to 29 are lighted on to have apredetermined light amount (e.g., a minimum light amount). After anelapse of the predetermined time period T, cancellation of the dimmingsignal is released, and the light-emitting diodes 26 to 29 are lightedon to have a light amount instructed by the dimming signal. Therefore,the influence of the dimming signal can be surely excluded only duringthe predetermined time period T from the timing immediately afterpower-ON, and a phenomenon of causing a full light state only for amoment immediately after activation due to an output delay of thedimming signal can be avoided. As a result, a natural lighting state asthe lighting equipment can be obtained, thus improving themerchantability of the lighting equipment.

(Modification 1)

In the aforementioned embodiment, the light-emitting diodes 26 to 29 arelighted on to have a predetermined light amount (e.g., a minimum lightamount) only during the predetermined time period T from the timingimmediately after power-ON. After an elapse of the predetermined timeperiod T, the light-emitting diodes 26 to 29 are lighted on to have alight amount instructed by the dimming signal. However, for example,when the level of the reference signal Vref is further reduced to set asignal level (an operable level of the control circuit 44) as low as thelight-emitting diodes 26 to 29 cannot be lighted on, the light-emittingdiodes 26 to 29 are lighted off during the predetermined time period Tfrom the timing immediately after power-ON. After an elapse of thepredetermined time period T, the light-emitting diodes 26 to 29 can belighted on to have a light amount instructed by the dimming signal.

(Modification 2)

In order to allow the setting level of the reference signal Vref to bevariable, a dimming function that can arbitrary control the light amountof the light-emitting diodes 26 to 29, which are lighted on after anelapse of the predetermined time period T from the timing immediatelyafter power-ON can be provided to the power supply device.

(Modification 3)

Furthermore, a large time constant specified by the aforementionedresistor 41 and capacitor 42 may be set. Based on the dimming signal(VDIM) at the node A between the resistor 32 and phototransistor 332,the dimming output (Vdet) output to the node B between the resistor 41and capacitor 42 is slowly increased by taking a certain time.Therefore, when the time constant is set so that this dimming output(Vdet) gives a minimum level required to light on the light-emittingdiodes 26 to 29 after an elapse of the aforementioned predetermined timeperiod T to the control signal, the control circuit 44 can be controlledto fade in the luminance of the light-emitting diodes 26 to 29 by thecontrol signal Vcont having a level specified depending on an increasein dimming output (Vdet). In this modification, the differentiatingcircuit of the capacitor 36 and resistor 37, and the transistor 39,which form a circuit for canceling the dimming signal, can be omitted.

Second Embodiment

A power supply circuit according to the second embodiment of the presentinvention will be described below.

FIG. 5 shows a power supply circuit according to the second embodimentof the present invention. In FIG. 5, the same reference numerals denotethe same parts as in FIG. 3, and a description thereof will not berepeated.

In the circuit shown in FIG. 5, a series circuit of a capacitor 51 andresistor 52 is connected between ground and a node between a positiveoutput terminal of a full-wave rectifying circuit 15 and a ripplecurrent smoothing capacitor 16. The series circuit of the capacitor 51and resistor 52 forms a differentiating circuit, which generates anoutput at a node between the capacitor 51 and 52 for a predeterminedtime based on an output from the ripple current smoothing capacitor 16.To the node between the capacitor 51 and resistor 52, the base of atransistor 53 is connected. The emitter of this transistor 53 isgrounded, and the collector is connected to a capacitor 36. Thetransistor 53 is turned on for a predetermined time by the outputgenerated at the node between the capacitor 51 and resistor 52.

In the power supply circuit according to the second embodiment, when anAC power of an AC power supply 11 is supplied to the full-waverectifying circuit 15 upon power-ON of a lighting equipment, and anoutput is generated at the ripple current smoothing capacitor 16 basedon the output from the full-wave rectifying circuit 15, a differentiatedoutput is generated only for a predetermined short time period at thenode between the capacitor 51 and resistor 52. Therefore, during theoutput period of the differentiated output, the transistor 53 is turnedon. In response to ON of the transistor 53, a residual charge on thecapacitor 36 is forcibly discharged in a direction of an arrow D via adiode 38 and the transistor 53, thus resetting a differentiating circuitformed by the capacitor 36 and a resistor 37.

In this power supply circuit, immediately after power-ON, thedifferentiating circuit formed by the capacitor 36 and resistor 37 isforcibly reset. Therefore, a predetermined time period T specified bythe differentiating circuit formed by the capacitor 36 and resistor 37can be accurately set, and an operation for canceling a dimming signalduring the predetermined time period T from a timing immediately afterpower-ON can be stably realized.

As described above, according to the present invention, since thedimming signal is canceled only during the predetermined time from thetiming immediately after power-ON, a phenomenon of causing a full lightstate only for a moment immediately after activation due to an outputdelay of the dimming signal can be avoided, thus obtaining a stablelighting state.

According to the present invention, during the predetermined time inwhich the dimming signal is canceled from the timing immediately afterpower-ON, semiconductor light-emitting elements can be set in one oflight-on, light-off, and dimmed lighting states.

Likewise, according to the present invention, since the differentiatingcircuit used to decide the predetermined time in which the dimmingsignal is canceled can be forcibly reset, the operation for cancelingthe dimming signal can be stably attained.

Note that in the aforementioned embodiment, immediately after power-ON,the differentiating circuit formed by the capacitor 36 and resistor 37is forcibly reset, and such operation may be performed at the time of apower-OFF operation or a light-off operation in response to an externalsignal.

In addition, the present invention is not limited to the aforementionedembodiments, and various modifications may be made without departingfrom the scope of the invention when it is practiced. For example, inthe aforementioned embodiments, light-emitting diodes have beenexemplified as semiconductor light-emitting elements. However, thepresent invention is applicable to a case using other semiconductorlight-emitting elements such as laser diodes. Also, in theaforementioned embodiments, the power supply circuit including the ACpower supply 11 has been described. However, the AC power supply 11 maybe arranged outside the device. Furthermore, in the aforementionedembodiments, an analog circuit has been exemplified. However, a controlmethod using a microcomputer and digital processing may be adopted.

The embodiments can provide a power supply device which assures a stablelighting state of a semiconductor light-emitting element, and a lightingequipment.

According to the embodiments, a lighting equipment can also be provided,which can obtain a stable lighting state of semiconductor light-emittingelements.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A power supply device for use in supplying powerto a semiconductor light-emitting element in response to a switchactivation, the power supply device comprising: a DC output generationmodule configured to receive AC power, convert the AC power into DCpower, and output the DC power; a semiconductor light-emitting elementconfigured to receive the DC power output from the DC output generationmodule, and to emit light; a receiving part configured to receive adimming signal which is output from a dimming signal generator; and acontrol module including a timer and configured to control the DC outputgeneration module to dim the semiconductor light-emitting element inaccordance with the dimming signal received at the receiving part onlyafter a predetermined time period from the switch activation asdetermined based on the timer, wherein the DC output generation modulecomprises first and second secondary windings, the first secondarywinding configured to provide power to the semiconductor light-emittingelement, and wherein the second secondary winding is configured toprovide power to the control module.
 2. The power supply device of claim1, wherein the switch activation corresponds to a time at which AC powerstarts being supplied to the DC output generation module.
 3. The powersupply device according to claim 1, wherein the control module isfurther configured to control the DC output generation module to performfade-in lighting of the semiconductor light-emitting element during thepredetermined time period.
 4. A lighting equipment comprising: the powersupply device according to claim 1; and an equipment main body havingthe power supply device.
 5. The power supply device of claim 1, whereinthe control module causes the semiconductor light-emitting element tolight on in a full light state, when no dimming signal is input to thecontrol module.